1. Field of the Invention
The present invention relates to a communication facility and a method for changing a control channel frequency, relating to a radio communication technology between a broadcast station and a mobile station.
2. Description of the Related Art
In the past, when an interference signal with the currently engaged control channel is detected by a base station in a central exchange cordless system, each base station acted independently to change the control channel frequency by seeking an available frequency and time slot. For example, a Japanese Patent Application, First Publication, H1-95630 discloses a technology to avoid communication errors due to interference signals.
However, operating within such a conventional technology, if several base stations try to switch to the same frequency and time slot, a problem of abnormality is experienced in the down-signal control channel towards the mobile station. The reason is that, in the conventional central exchange cordless system, when any base station detects an interference signal against its own control channel, each base station is able to alter the frequency and time slot according to its own judgment without regard to the operating conditions of other base stations, resulting in overloading and demodulation conflicts in a particular control channel frequency.